Resistance variable nonvolatile memory device

ABSTRACT

Each of memory cells (MC) includes one transistor and one resistance variable element. The transistor includes a first main terminal, a second main terminal and a control terminal. The resistance variable element includes a first electrode, a second electrode and a resistance variable layer provided between the first electrode and the second electrode. A first main terminal of one of two adjacent memory cells is connected to a second main terminal of the other memory cell, to form a series path (SP) sequentially connecting main terminals of the plurality of memory cells in series. Each of the memory cells is configured such that the control terminal is a part of a first wire (WL) associated with the memory cell or is connected to the first wire associated with the memory cell, the second electrode is a part of a second wire (SL) associated with the memory cell or is connected to the second wire associated with the memory cell; and the first electrode is a part of a series path (SP) associated with the memory cell or is connected to the series path associated with the memory cell.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application No. PCT/JP2010/001833, filed on Mar. 15, 2010,which in turn claims the benefit of Japanese Application No.2009-074572, filed on Mar. 25, 2009, the disclosures of whichApplications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a resistance variable nonvolatilememory device including a memory cell configured to include a resistancevariable element which changes resistance values reversibly in responseto electric signals and a transistor.

BACKGROUND ART

In recent years, a nonvolatile memory device incorporating a memory cellconfigured to include a resistance variable element has been studied anddeveloped. As used herein, the resistance variable element refers to anelement which has a characteristic in which its resistance values changereversibly in response to electric signals and is capable of storingdata corresponding to the resistance values in a nonvolatile manner.

The memory cell including the resistance variable element is configuredin, for example, a cross-point structure. In the cross-point structure,memory cells are respectively arranged at cross points of bit lines andword lines which cross each other in a direction perpendicular to eachother such that each memory cell is sandwiched between the associatedbit line and the associated word line. A practicable area of the memorycell is 4F². Patent literature 1 discloses a cross-point resistancevariable memory device incorporating a bipolar resistance variableelement. In this resistance variable memory device, when data iswritten, Vpp is applied to a selected bit line, Vss (0V) is applied to aselected word line, and 1/2Vpp is applied to an unselected word line andto an unselected bit line, while when data is erased, Vpp is applied toa selected word line, Vss (0V) is applied to a selected bit line, andVpp/2 is applied to an unselected word line and to an unselected bitline.

As a nonvolatile memory device incorporating the resistance variableelement, a nonvolatile memory device is generally known, in which 1T1Rmemory cells are arrayed in matrix at intersections of bit lines, wordlines, and source lines, and the word lines and the source linesextending in a direction perpendicular to the bit lines, such that eachmemory cell includes a MOS transistor and a resistance variable elementwhich are coupled to each other in series. A necessary area of thememory cell is 6F² at least.

Patent literature 2 discloses a nonvolatile memory device including a1T1R memory cell comprising oxide having a perovskite crystallinestructure as a resistance variable element.

FIG. 47 is a schematic view of a cross-section of the memory celldisclosed in FIG. 2 of Patent literature 2.

A memory cell 1011 includes a transistor 1006 and a resistance variableelement 1010 which are electrically connected to each other in series.

The transistor 1006 includes on a semiconductor substrate 1001, a sourceregion 1002 which is a first diffusion layer region, a drain region 1003which is a second diffusion layer region, and a gate electrode 1005formed on a gate oxide layer 1004.

The resistance variable element 1010 includes a resistance variablelayer 1008 which changes resistance values in response to voltagesapplied, a lower electrode 1007, and an upper electrode 1009 such thatthe resistance variable layer 1008 is sandwiched between the lowerelectrode 1007 and the upper electrode 1009.

The drain region 1003 is electrically connected to the lower electrode1007.

The upper electrode 1009 is connected to a metal wire which serves as abit line 1012, the gate electrode 1005 is connected to a word line, andthe source region 1002 is connected to a metal wire which serves as asource line 1013.

As a material used for the resistance variable layer 1008,Pr_(1−x)Ca_(x)MnO₃, La_(1−x)Ca_(x)MnO₃ (LCMO) and other materials aredisclosed, but an electrode material is not mentioned specifically.

A method of writing data to the memory cell 1011, is also disclosed, inwhich the resistance variable layer 1008 changes from a low-resistancestate to a high-resistance state when Vpp is applied to the upperelectrode 1009, Vss is applied to the source region 1002, and a pulsevoltage with a specified voltage amplitude Vwp is applied to the gateelectrode, while the resistance variable layer 1008 changes from thehigh-resistance state to the low-resistance state when Vss is applied tothe upper electrode 1009, Vpp is applied to the source region 1002, anda pulse voltage with a specified voltage amplitude Vwe is applied to thegate electrode.

Patent literature 3 and Patent literature 4 disclose a structure forachieving an area of memory cell of 4F² using the 1T1R memory structure.

FIG. 48 is a circuit diagram disclosed in FIG. 5 of Patent literature 3.As shown, a memory cell is configured to include a resistance variableelement and a transistor which are arranged in parallel. A memory arrayis configured by connecting memory cells in series. With thisarrangement, the area of the memory cell is determined by the area ofthe transistor and can be reduced to 4F² in practice.

CITATION LIST Patent Literatures

Patent literature 1: Japanese Laid-Open Patent Application PublicationNo. 2006-203098

Patent literature 2: Japanese Laid-Open Patent Application PublicationNo. 2005-25914

Patent literature 3: Japanese Laid-Open Patent Application PublicationNo. 2004-272975

Patent literature 4: U.S. Pat. No. 7,298,640 specification

SUMMARY OF THE INVENTION Solution to Problem

However, Patent literature 1 reciting that the area of the memory cellsmaller than the area of 1T1R memory cell of 6F², discloses thecross-point resistance variable memory device including a varistor as arectifying element. In general, a cross-point resistance variable memorydevice uses a diode as the rectifying element. The diode has acharacteristic in which its current increases exponentially with respectto a voltage. A value of the current flowing through the diode does notfully reach zero even when an applied voltage is lower than a thresholdvoltage Vth. In a case where an electric potential difference of Vpp/2is applied to an unselected memory cell as recited in Patent literature1, a current flowing through the unselected cell is about one hundredthto about one thousandth of the current flowing through the selectedcell, if Schottky or MIM diode model is used. In a large-scale memoryarray, several hundreds to several thousands memory cells are arrangedalong one row or one column. Therefore, a total current flowing throughunselected cells connected to a selected bit line or selected word line(leak current) is not always negligible as compared to a value of thecurrent flowing through a selected cell.

In Patent literature 3 and Patent literature 4, since the resistancevariable element and the transistor are arranged in parallel, all oftransistors disposed along the same column are turned ON and asource-drain voltage is applied to unselected resistance variableelements, when one memory cell is selected from among the memory cellsarranged in series. In addition, the resistance of the resistancevariable element in a low-resistance state is several hundreds Ω and theON-resistance of the transistor is about 1 kΩ, and therefore, a morecurrent flows in amount through the resistance variable element in a lowresistance state than the transistor, which deteriorates a memorycharacteristic of the element.

The present invention has been made to solve the above describedproblem, and a primary object of the present invention is to provide anonvolatile memory device which devises a structure for positioning aresistance variable element to implement a memory cell of 4F² whileeffectively suppressing a current flowing through an unselected memorycell.

Solution to Problem

To solve the above described problem, a nonvolatile memory device of thepresent invention comprises a plurality of first wires extending inparallel with each other in a first direction within a first plane; aplurality of second wires extending in parallel with each other in asecond direction within a second plane parallel to the first plane suchthat the plurality of second wires three-dimensionally cross theplurality of first wires, respectively; and memory cells provided torespectively correspond to three-dimensional cross-points of the firstwires and the second wires; each of the memory cells including onetransistor and one resistance variable element; the transistor includinga first main terminal, a second main terminal and a control terminal;the resistance variable element including a first electrode, a secondelectrode and a resistance variable layer provided between the firstelectrode and the second electrode; the memory cells including aplurality of memory cells which are arranged along the first directionand configured such that a first main terminal of one of two adjacentmemory cells is connected to a second main terminal of the other memorycell, to form a series path extending in the first direction andsequentially connecting main terminals of the plurality of memory cellsin series; and each of the memory cells being configured such that: thecontrol terminal is connected to a first wire associated with the memorycell; the second electrode is connected to a second wire associated withthe memory cell; and the first electrode is connected to a series pathassociated with the memory cell.

In such a configuration, it is possible to provide a nonvolatile memorydevice which implements a memory cell of 4F² while effectivelysuppressing a current flowing through an unselected memory cell.

The nonvolatile memory device may further comprise a plurality of thirdwires extending in parallel with each other in the first direction. Theplurality of memory cells arranged along the first direction may form aplurality of memory blocks each of which includes a predetermined numberof memory cells arranged successively. The series path may be connectedto the associated third wire for each of the memory blocks.

In such a configuration, a wire delay in the series path can besuppressed by using an electric conductor with a low resistivity for abit line BL.

In the nonvolatile memory device, both ends of the series path may beconnected to the associated third wire for each of the memory blocks.

In such a configuration, since the electric potential propagates fromthe both sides of the series path, the wire delay can be suppressed moreeffectively.

The nonvolatile memory device may further comprise an electric powersupply circuit for applying voltages to the resistance variable elementincluded in each of the memory cells. The electric power supply circuitmay be configured to change output voltages, according to the number oftransistors included in a portion of a series path associated with aselected memory cell, from a connecting point of the associated seriespath and the associated third wire to the first electrode of theselected memory cell.

In such a configuration, the voltages applied between the electrodes ofthe resistance variable element are constant irrespective of thelocation of the memory cell. Therefore, it is possible to uniformize therespective resistance values after writing and to suppress anunnecessary voltage stress applied to the resistance variable elementmore effectively, as compared to the conventional configuration.

In the nonvolatile memory device, each of the first main terminal andthe second main terminal may include a silicide layer; and the silicidelayer may constitute the first electrode.

In the nonvolatile memory device, the silicide layer may compriseplatinum silicide.

The above and further objects, features and advantages of the presentinvention will more fully be apparent from the following detaileddescription of preferred embodiments with reference to accompanyingdrawings.

Advantageous Effects of the Invention

The present invention has the above described configuration, and canprovide a a nonvolatile memory device which implements a memory cell of4F² while suppressing a current flowing through an unselected memorycell more effectively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an exemplary circuit configuration ofa nonvolatile memory device 100 according to Embodiment 1 of the presentinvention.

FIG. 2 is an enlarged view of a memory cell MC of FIG. 1, in whichsubscripts indicate a row and column of the associated memory block.

FIG. 3 is a view showing one memory block, in which FIG. 3( a) is a topplan view of the memory block and FIG. 3( b) is an equivalent circuitdiagram of FIG. 3( a).

FIG. 4 is a cross-sectional view of the memory block indicated byone-dotted line of FIG. 3, in which FIG. 4( a) is a cross-sectional viewtaken along line A-A′ of FIG. 3, FIG. 4( b) is a cross-sectional viewtaken along line B-B′ of FIG. 3, FIG. 4( c) is a cross-sectional viewtaken along C-C′ of FIG. 3, FIG. 4( d) is a cross-sectional view takenalong line D-D′ of FIG. 3, FIG. 4( e) is a cross-sectional view takenalong line E-E′ of FIG. 3, and FIG. 4( f) is a cross-sectional viewtaken along line F-F′ of FIG. 3.

FIG. 5 is a view showing an exemplary characteristic (relationshipbetween voltages and resistance values) of a resistance variable elementincluded in a nonvolatile memory device according to Embodiment 1 of thepresent invention.

FIG. 6 is a timing chart showing an exemplary operation of thenonvolatile memory device according to Embodiment 1 of the presentinvention, in which FIG. 6( a) shows an operation in which “0” iswritten (resistance variable element RR is changed to a low-resistancestate) to a memory cell MC00 ₀₀, FIG. 6( b) shows an operation in which“1” is written (resistance variable element RR is changed to ahigh-resistance state) to the memory cell MC00 ₀₀, and FIG. 6( c) showsan operation in which data is read from the memory cell MC00 ₀₀.

FIG. 7 is a top plan view showing the step of forming a polysiliconlayer on a P-type silicon substrate.

FIG. 8 is cross-sectional views showing the step of forming thepolysilicon layer on the P-type silicon substrate, in which FIG. 8( a)is a cross-sectional view taken in the direction of arrows along A-A′ ofFIG. 7, FIG. 8( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 7, FIG. 8( c) is a cross-sectional view takenin the direction of arrows along C-C′ of FIG. 7, FIG. 8( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.7, FIG. 8( e) is a cross-sectional view taken in the direction of arrowsalong E-E′ of FIG. 7, and FIG. 8( f) is a cross-sectional view taken inthe direction of arrows along F-F′ of FIG. 7.

FIG. 9 is a top plan view showing the step of etching the P-type siliconsubstrate and the polysilicon layer to form a trench into which STI isfilled.

FIG. 10 is cross-sectional views showing the step of etching the P-typesilicon substrate and the polysilicon layer to form the trench intowhich the STI is filled, in which FIG. 10( a) is a cross-sectional viewtaken in the direction of arrows along A-A′ of FIG. 9, FIG. 10( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.9, FIG. 10( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 9, FIG. 10( d) is a cross-sectional view takenin the direction of arrows along D-D′ of FIG. 9, FIG. 10( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.9, and FIG. 10( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 9.

FIG. 11 is a top plan view showing the step of filling silicon dioxideinto the trench to form the STI.

FIG. 12 is cross-sectional views showing the step of filling silicondioxide into the trench to form the STI, in which FIG. 12( a) is across-sectional view taken in the direction of arrows along A-A′ of FIG.11, FIG. 12( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 11, FIG. 12( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 11, FIG. 12( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.11, FIG. 12( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 11, and FIG. 12( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 11.

FIG. 13 is a top plan view showing the step of forming a Si₃N₄ layer tocover the silicon dioxide layer and the polysilicon layer.

FIG. 14 is a cross-sectional views showing the step of forming the Si₃N₄layer to cover the silicon dioxide layer and the polysilicon layer, inwhich FIG. 14( a) is a cross-sectional view taken in the direction ofarrows along A-A′ of FIG. 13, FIG. 14( b) is a cross-sectional viewtaken in the direction of arrows along B-B′ of FIG. 13, FIG. 14( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.13, FIG. 14( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 13, FIG. 14( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 13, and FIG. 14( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 13.

FIG. 15 is a top plan view showing the step of forming a memory trench.

FIG. 16 is cross-sectional views showing the step of forming the memorytrench, in which FIG. 16( a) is a cross-sectional view taken in thedirection of arrows along A-A′ of FIG. 15, FIG. 16( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.15, FIG. 16( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 15, FIG. 16( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 15, FIG. 16( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.15, and FIG. 16( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 15.

FIG. 17 is a top plan view showing the step of implanting phosphorousatoms (P) into a region of the bottom surface of each memory trench,where the P-type silicon substrate is exposed.

FIG. 18 is cross-sectional views showing the step of implanting thephosphorous atoms (P) into the region of the bottom surface of eachmemory trench, where the P-type silicon substrate is exposed, in whichFIG. 18( a) is a cross-sectional view taken in the direction of arrowsalong A-A′ of FIG. 17, FIG. 18( b) is a cross-sectional view taken inthe direction of arrows along B-B′ of FIG. 17, FIG. 18( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.17, FIG. 18( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 17, FIG. 18( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 17, and FIG. 18( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 17.

FIG. 19 is a top plan view showing the step of forming Si₃N₄ portions(side walls) on right and left side walls of each memory trench.

FIG. 20 is cross-sectional views showing the step of forming the Si₃N₄portions (side walls) on the right and left side walls of each memorytrench, in which FIG. 20( a) is a cross-sectional view taken in thedirection of arrows along A-A′ of FIG. 19, FIG. 20( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.19, FIG. 20( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 19, FIG. 20( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 19, FIG. 20( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.19, and FIG. 20( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 19.

FIG. 21 is a top plan view showing the step of implanting phosphorousatoms (P) into a region between a pair of Si₃N₄ portions formed on eachmemory trench, where the P-type silicon substrate is exposed.

FIG. 22 is cross-sectional views showing the step of implanting thephosphorous atoms (P) into the region between the pair of Si₃N₄ portionsformed on each memory trench, where the P-type silicon substrate isexposed, in which FIG. 22( a) is a cross-sectional view taken in thedirection of arrows along A-A′ of FIG. 21, FIG. 22( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.21, FIG. 22( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 21, FIG. 22( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 21, FIG. 22( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.21, and FIG. 22( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 21.

FIG. 23 is a top plan view showing the step of forming a platinumsilicide layer into a region between the pair of Si₃N₄ portions formedon each memory trench, where the P-implanted region is exposed.

FIG. 24 is cross-sectional views showing the step of forming theplatinum silicide layer into the region between the pair of Si₃N₄portions formed on each memory trench, where the P-implanted region isexposed, in which FIG. 24( a) is a cross-sectional view taken in thedirection of arrows along A-A′ of FIG. 23, FIG. 24( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.23, FIG. 24( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 23, FIG. 24( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 23, FIG. 24( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.23, and FIG. 24( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 23.

FIG. 25 is a top plan view showing the step of forming a tantalum oxidelayer and a tantalum nitride layer over an entire surface including sidesurfaces and a bottom surface of each memory trench.

FIG. 26 is cross-sectional views showing the step of forming thetantalum oxide layer and the tantalum nitride layer over the entiresurface including the side surfaces and the bottom surface of eachmemory trench, in which FIG. 26( a) is a cross-sectional view taken inthe direction of arrows along A-A′ of FIG. 25, FIG. 26( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.25, FIG. 26( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 25, FIG. 26( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 25, FIG. 26( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.25, and FIG. 26( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 25.

FIG. 27 is a top plan view showing the step of removing the tantalumoxide layer and the tantalum nitride layer except for the portion of thetantalum oxide layer and the portion of the tantalum nitride layer whichare present inside the memory trench.

FIG. 28 is a cross-sectional view showing the step of removing thetantalum oxide layer and the tantalum nitride layer except for theportion of the tantalum oxide layer and the portion of the tantalumnitride layer which are present inside the memory trench, in which FIG.28( a) is a cross-sectional view taken in the direction of arrows alongA-A′ of FIG. 27, FIG. 28( b) is a cross-sectional view taken in thedirection of arrows along B-B′ of FIG. 27, FIG. 28( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.27, FIG. 28( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 27, FIG. 28( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 27, and FIG. 28( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 27.

FIG. 29 is a top plan view showing the step of forming a tungsten layerinto a trench formed inside the tantalum nitride layer and forming asilicon dioxide layer into a recess.

FIG. 30 is cross-sectional views showing the step of forming thetungsten layer into the trench formed inside the tantalum nitride layerand forming the silicon dioxide layer into the recess, in which FIG. 30(a) is a cross-sectional view taken in the direction of arrows along A-A′of FIG. 29, FIG. 30( b) is a cross-sectional view taken in the directionof arrows along B-B′ of FIG. 29, FIG. 30( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 29, FIG. 30( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.29, FIG. 30( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 29, and FIG. 30( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 29.

FIG. 31 is a top plan view showing the step of forming a silicon dioxidelayer over the entire surface and forming a trench into which a wordline is filled.

FIG. 32 is cross-sectional views showing the step of forming the silicondioxide layer over the entire surface and forming the trench into whichthe word line is filled, in which FIG. 32( a) is a cross-sectional viewtaken in the direction of arrows along A-A′ of FIG. 31, FIG. 32( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.31, FIG. 32( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 31, FIG. 32( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 31, FIG. 32( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.31, and FIG. 32( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 31.

FIG. 33 is a top plan view showing the step of forming a hole into whicha control electrode (gate) of a transistor is filled.

FIG. 34 is cross-sectional views showing the step of forming the holeinto which the control electrode (gate) of the transistor is filled, inwhich FIG. 34( a) is a cross-sectional view taken in the direction ofarrows along A-A′ of FIG. 33, FIG. 34( b) is a cross-sectional viewtaken in the direction of arrows along B-B′ of FIG. 33, FIG. 34( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.33, FIG. 34( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 33, FIG. 34( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 33, and FIG. 34( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 33.

FIG. 35 is a top plan view showing the step of forming the word line andthe control electrode (gate) of the transistor.

FIG. 36 is cross-sectional views showing the step of forming the wordline and the control electrode (gate) of the transistor, in which FIG.36( a) is a cross-sectional view taken in the direction of arrows alongA-A′ of FIG. 35, FIG. 36( b) is a cross-sectional view taken in thedirection of arrows along B-B′ of FIG. 35, FIG. 36( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.35, FIG. 36( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 35, FIG. 36( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 35, and FIG. 36( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 35.

FIG. 37 is a top plan view showing the step of forming a trench intowhich the source line is filled and a hole into which a contact isfilled.

FIG. 38 is cross-sectional views showing the step of forming the trenchinto which the source line is filled and the hole into which the contactis filled, in which FIG. 38( a) is a cross-sectional view taken in thedirection of arrows along A-A′ of FIG. 37, FIG. 38( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.37, FIG. 38( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 37, FIG. 38( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 37, FIG. 38( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.37, and FIG. 38( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 37.

FIG. 39 is a top plan view showing the step of forming the source lineand the contact.

FIG. 40 is cross-sectional views showing the step of forming the sourceline and the contact, in which FIG. 40( a) is a cross-sectional viewtaken in the direction of arrows along A-A′ of FIG. 39, FIG. 40( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.39, FIG. 40( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 39, FIG. 40( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 39, FIG. 40( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.39, and FIG. 40( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 39.

FIG. 41 is a top plan view showing the step of forming the bit line anda contact.

FIG. 42 is cross-sectional views showing the step of forming the bitline and the contact, in which FIG. 42( a) is a cross-sectional viewtaken in the direction of arrows along A-A′ of FIG. 41, FIG. 42( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.41, FIG. 42( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 41, FIG. 42( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 41, FIG. 42( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.41, and FIG. 42( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 41.

FIG. 43 is a block diagram showing an exemplary circuit configuration ofa nonvolatile memory device 100′ according to Modification Example ofEmbodiment 1 of the present invention.

FIG. 44 is a block diagram showing an exemplary circuit configuration ofa nonvolatile memory device 200 according to Embodiment 2 of the presentinvention.

FIG. 45 is a conceptual view for simulating an electric potential dropbecause of a substrate bias effect.

FIG. 46 is a view showing result of the electric potential drop becauseof the substrate bias effect, which is obtained by conducting asimulation based on the conceptual view of FIG. 45.

FIG. 47 is a schematic view of a cross-section of a memory celldisclosed in Patent literature 2.

FIG. 48 is a circuit diagram disclosed in Patent literature 3.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the drawings.

Embodiment 1

[Device Configuration]

FIG. 1 is a block diagram showing an exemplary circuit configuration ofa nonvolatile memory device 100 according to Embodiment 1 of the presentinvention. FIG. 2 is an enlarged view of a memory cell MC of FIG. 1, inwhich subscripts indicate a row and column of the associated memoryblock.

As shown in FIGS. 1 and 2, the nonvolatile memory device 100 includes aplurality of word lines WL0 ₀, WL1 ₀, WL2 ₀, WL3 ₀, WL1 ₀, WL1 ₁, . . .(first wires comprising, for example, tungsten: hereinafter simplyreferred to as “WL”) extending in parallel with each other in a firstdirection within a first plane, a plurality of source lines SL0 ₀, SL1₀, SL2 ₀ SL3 ₀, SL0 ₁, SL1 ₁, . . . (second wires comprising, forexample, copper: hereinafter simply referred to as “SL”) extending inparallel with each other in a second direction within a second planeparallel to the first plane to three-dimensionally cross the firstwires, and memory cells MC00 ₀₀, MC01 ₀₀, MC02 ₀₀, MC03 ₀₀, MC10 ₀₀, . .. MC33 ₀₀, . . . MC32 _(mn), MC33 _(mn) (hereinafter simply referred toas “MC”) arranged to respectively correspond to three-dimensionalcross-points of the word lines WL and the source lines SL.

Each of the memory cells MC includes one transistor TR (e.g., FETtransistor) and one resistance variable element RR (e.g., ReRAMelement). Each transistor TR includes a first main terminal T1(source/drain), a second main terminal T2 (source/drain) and a controlterminal T3 (gate). Each resistance variable element RR includes a firstelectrode E1 (lower electrode comprising, for example, platinum orplatinum silicide), a second electrode E2 (upper electrode comprising,for example, tantalum nitride), and a resistance variable layer VR(comprising, for example, oxide of transition metal such as Ta, Ni, Ti,Hf, or Zr, preferably comprising tantalum oxide, and more preferablymade of tantalum oxide) provided between the first electrode E1 and thesecond electrode E2.

A plurality of memory cells MC arranged along the first direction areconfigured such that the first main terminal T1 of one memory cell MCincluded in two adjacent memory cells MC and the second main terminal T2of the other memory cell MC are connected to each other, thereby formingseries paths SP0 ₀₀, SP1 ₀₀, SP2 ₀₀, SP3 ₀₀, SP0 ₀₁, . . . (hereinaftersimply referred to as “SP”) extending in the first direction andsequentially connecting the main terminals of the plurality of memorycells in series.

The control terminal T3 of each memory cell MC is connected to the wordline WL associated with the memory cell MC.

The second electrode E2 of each memory cell MC is connected to thesource line SL associated with the memory cell MC. The second electrodeE2 may be a part of the source line SL associated with the memory cellMC.

The first electrode E1 of each memory cell MC is connected to the seriespath SP associated with the memory cell MC. The first electrode E1 maybe a part of the series path SP associated with the memory cell MC.

In such a configuration, one resistance variable element is provided forone transistor. In other words, two adjacent resistance variableelements share one transistor at their first electrodes E1 and theirsecond electrodes E2 are not connected to the transistor but to thewire. A current fed to a selected memory cell flows through the seriespath SP, but does not flow between the electrodes of an unselectedmemory cell. In such a configuration, it is possible to implement anonvolatile memory device having a 1T1R memory cell array includingmemory cells of 4F² while effectively suppressing a current flowingthrough an unselected memory cell.

The nonvolatile memory device 100 further includes a plurality of bitlines BL0, BL1, . . . (third wire comprising, for example, copper:hereinafter simply referred to as “BL”) extending in parallel with eachother in the first direction. The plurality of memory cells MC arrangedalong the first direction are configured such that a predeterminednumber of memory cells MC arranged successively constitute each of aplurality of memory blocks MB. For each memory block MB, the seriespaths SP are connected to the bit line BL via a contact wire CL(comprising, for example, platinum silicide: hereinafter simply referredto as “CL”) extending in the second direction.

In such a configuration, a wire delay in the series path can besuppressed by using an electric conductor with a low resistivity as thebit line BL.

In this embodiment, each of the first main terminal T1 and the secondterminal T2 includes a silicide layer which constitutes the firstelectrode E1. The silicide layer preferably comprises platinum silicide.

In such a configuration, since the silicide formed on the siliconsubstrate is used as the electrode of the resistance variable element,the size of the element can be further reduced. Especially, sinceplatinum is suitable for use as an electrode material of the resistancevariable element, the silicide layer preferably comprises platinumsilicide.

The source lines SL are each connected to a column decoder 102. The wordlines WL and the bit lines BL are each connected to a row decoder 104.The memory cells MC, the word lines WL, the source lines SL, the bitlines BL, the contact wires CL, the column decoder 102 and the rowdecoder 104 constitute one memory cell array 106, as a whole.

The memory cell array 106 includes memory blocks MB of m rows and ncolumns. Each memory block MB includes (4×4=16) memory cells MC. Thememory cell array 106 entirely includes 16 mn memory cells MC. Thenumber of word lines WL is 4 m, the number of source lines is 4 n, thenumber of bit lines is m, and the number of contact wires CL is n.

The memory cells MC belonging to a memory cell block MB_(xy) on the samecolumn (y column) are configured such that the memory cells MC belongingto the same column number (column number in 4×4 matrix) within thememory cell block MB_(xy) are connected to one another via an identicalsource line SL. To be specific, for example, the memory cells (MC00 ₀₀,MC10 ₀₀, MC20 ₀₀, MC30 ₀₀, MC00 ₁₀, . . . ) on the first line (firstcolumn) from the left, belonging to the memory cell block MB_(xo) on thefirst column are connected to one another via an identical source lineSL0 ₀, while the memory cells (MC01 ₀₀, MC11 ₀₀, MC21 ₀₀, MC31 ₀₀, MC01₁₀, . . . ) on the second line (second column) from the left areconnected to one another via an identical source line SL1 ₀.

The nonvolatile memory device 100 further includes an address inputcircuit 108 which receives address signals AD from outside and transferthem to the memory cell array 106, a control circuit 110 which receivesa control signal CTL from outside and transfers it to the memory cellarray 106, an electric power supply circuit 112 which outputspredetermined voltages (write voltages such as low-resistance stateattaining voltage and high-resistance state attaining voltage, readvoltage, etc), a data input/output circuit 114 which receives andoutputs data from and to outside, a write circuit 116 which outputsvoltages from the electric power supply circuit 112 to the memory cellarray, based on the write data output from the data input/outputcircuit, and a sense amplifier 120. The sense amplifier 120 detects anamount of current flowing through a selected bit line, and determinesthat data is “1” when the detected current amount corresponds to a statewhere the memory cell is in a high-resistance state and data is “0” whenthe detected current amount corresponds to a state where the memory cellis in a low-resistance state.

The electric power supply circuit 112 includes a low-resistance stateattaining voltage generating circuit 122 for generating a voltageapplied to change the memory cell MC to the low-resistance state (changethe resistance variable element RR included in the memory cell MC to thelow-resistance state), and a high-resistance state attaining voltagegenerating circuit 124 for generating a voltage applied to change thememory cell MC to the high-resistance state (change the resistancevariable element RR included in the memory cell MC to thehigh-resistance state).

[Schematic Configuration of Memory Block]

FIG. 3 is a view showing one memory block, in which FIG. 3( a) is a topplan view of the memory block and FIG. 3( b) is an equivalent circuitdiagram of FIG. 3( a). FIG. 3( b) shows an enlarged view of the memoryblock MB extracted from FIG. 1.

As shown in FIG. 3( a), the word lines WL (first wires) extend inparallel with each other in the first direction (rightward and leftwarddirection in FIG. 3( a)) within the first plane, the source lines SL(second wires) extend in parallel with each other in the seconddirection (upward and downward direction in FIG. 3( a)) within a secondplane parallel to the first plane and three-dimensionally cross the wordlines WL, the bit lines BL (third wires) extend in parallel with eachother in the first direction (rightward and leftward direction in FIG.3( a)) within a third plane parallel to the second plane, and thecontact wires CL (fourth wires) extend in parallel with each other inthe second direction (upward and downward direction in FIG. 3( a))within a fourth plane parallel to the third plane.

The memory cell MC, the first main terminal T1 of the transistor TR andthe second main terminal T2 of the transistor TR are provided at thethree-dimensional cross-point of the word line WL and the source lineSL. The control terminal T3 of the transistor TR is provided at aportion of the word line WL which does not overlap with the source lineSL.

A contact C1 (connecting portion of the source line SL and the secondelectrode E2) is provided below the three-dimensional cross-point of thebit line BL and the source line SL. As described later, in thisembodiment, the second electrode E2 extends in the second direction andserves as upper electrodes of a plurality of resistance variableelements RR. Although it looks like that the second electrode E2 isconnected to the source line SL for each memory cell in the equivalentcircuit diagram (FIG. 3 b), the second electrode E2 is actuallyconnected to the source line SL for each memory cell block. Nonetheless,the circuit is actually equivalent to that shown in FIG. 3( b).

A contact C2 (connecting portion of the bit line BL and the contact wireCL) is provided at three-dimensional cross-point of the bit line BL andthe contact wire CL.

[Configuration of Cross-Section of Memory Block]

FIG. 4 is a cross-sectional view of the memory block indicated byone-dotted line of FIG. 3, in which FIG. 4( a) is a cross-sectional viewtaken along line A-A′ of FIG. 3, FIG. 4( b) is a cross-sectional viewtaken along line B-B′ of FIG. 3, FIG. 4( c) is a cross-sectional viewtaken along C-C′ of FIG. 3, FIG. 4( d) is a cross-sectional view takenalong line D-D′ of FIG. 3, FIG. 4( e) is a cross-sectional view takenalong line E-E′ of FIG. 3, and FIG. 4( f) is a cross-sectional viewtaken along line F-F′ of FIG. 3. Hereinafter, in FIG. 4, the directionin which the source line SL extends is expressed as a forward andrearward direction, a thickness direction of the substrate is expressedas an upward and downward direction, and the direction in which the wordline WL extends is expressed as a rightward and leftward direction. Theportions indicated by the same mesh patterns in FIG. 4 mean that theycomprise substantially the same material in principle, but even theportions indicated by the same mesh patterns in FIG. 4 means that theyhave different compositions or contents in a strict sense, in somecases.

As shown in FIG. 4, in the memory block MB, a plurality of silicondioxide layers 132 are formed on the P-type silicon substrate layer 130to extend in the rightward and leftward direction at predeterminedintervals. It should be noted that the left end of the silicon dioxidelayer 132 extends continuously in the forward and leftward direction.The portion of the silicon dioxide layer 132, extending in the rightwardand leftward direction constitutes STI [Shallow Trench Insulator]region. The size of the STI region is, for example, 0.18 μm in width and300 nm in depth.

A plurality of trenches (hereinafter referred to as “memory trenches”:the number of the memory trenches is five in FIG. 4) are formed topenetrate the upper half portions of the silicon dioxide layers 132 andextend in the forward and rearward direction. The size of the memorytrench is for example, 0.18 μm in width and 550 nm in depth (STI plusheight of dummy gate). Si₃N₄ portions 138 (side walls) are formed onright and left side walls of the memory trench. A tantalum oxide layer140 (resistance variable layer) and a tantalum nitride layer 142 (upperelectrode layer) are formed in this order to cover the surfaces of theSi₃N₄ portions 138 and the bottom surface of the memory trench. Thethickness of the bottom portion of the tantalum oxide layer 140 is, forexample, 30 nm. A tungsten layer 144 (embedded electric conductor layer)is formed to fill the trench formed inside the tantalum nitride layer142. The Si₃N₄ portions 138, the tantalum oxide layer 140, the tantalumnitride layer 142 and the tungsten layer 144 are entirely filled intothe memory trench, their upper end surfaces define a recess, and asilicon dioxide layer 148 is filled into the recess. It should be notedthat a titanium/titanium nitride layer 149 (adhesive layer) is filledinto a recess in a portion (cross-section taken along C-C′) where acopper layer 154 (source line SL) is connected to the tantalum nitridelayer 142. The embedded electric conductor layer may comprise copper oraluminum.

A tungsten layer 152 forming the word line WL and a titanium/titaniumnitride layer 150 (adhesive layer) extend in the rightward and leftwarddirection above the region where the STI region is not present. The sizeof the tungsten layer 152 is, for example, 0.18 μm in width and 300 nmin depth. In a region where the memory trench is not present, thetungsten layer 152 and the titanium/titanium nitride layer 150 extenddownward and are connected to the P-type silicon substrate layer 130 viathe silicon dioxide layer 158. The thickness of the silicon dioxidelayer 158 is, for example, 10 nm. A region where the tungsten layer 152is connected to the P-type silicon substrate layer 130 via the silicondioxide layer 158 serves as the control terminal T3 (gate) of thetransistor TR. The size of the control terminal T3 is for example, 0.18μm×0.18 μm.

A P-implanted region 134 (source/drain region) is formed in a regionwhere the P-type silicon substrate layer 130 is connected to the memorytrench. A platinum silicide layer 136 is formed over the P-implantedregion 134. The P-implanted region 134 and the platinum silicide layer136 are formed inside the P-type silicon substrate layer 130. TheP-implanted region 134 may be replaced by an As-implanted region(phosphorous atoms [P] may be replaced by arsenic atoms [As]).

The rightmost memory trench (hereinafter referred to as contact wiretrench), among five memory trenches, is not provided with the silicondioxide layer 132 even in the STI region and is connected to the P-typesilicon substrate layer 130. The P-implanted region 134 and the platinumsilicide layer 136 are formed continuously (to extend in the forward andrearward direction) on the bottom surface of the contact wire trench.The platinum silicide layer 136 connected to the contact wire trenchconstitutes the contact wire CL.

The platinum silicide layer 136 connected to the memory trench otherthan the contact wire trench constitutes the lower electrode layer(first electrode E1). A portion of the tantalum nitride layer 142 whichcorresponds to the lower electrode layer serves as the second electrodeE2. A portion of the tantalum oxide layer 140 which is sandwichedbetween the lower electrode layer and the upper electrode layer servesas the resistance variable layer VR. In the cross-section taken alongA-A′, the P-implanted region 134 and the platinum silicide layer 136serve as the first main terminal T1 (source/drain) of the transistor TRand the second main terminal T2 (source/drain) of the transistor TR.

In the cross-section taken along A-A′, a region (gate) where thetungsten layer 152 is connected to the P-type silicon substrate layer130 via the silicon dioxide layer 158 and a region (source/drain)comprising the P-implanted region 134 and the platinum silicide layer136 are arranged continuously alternately in the rightward and leftwarddirection, thereby forming one series path SP. The platinum silicidelayer 136 constitutes a part of the series path SP as well as the lowerelectrode of the resistance variable element RR. The P-implanted region134 which is a constituent of the first main terminal T1 and the secondmain terminal T2 of the transistor TR also constitutes a part of theseries path SP.

A plurality of copper layers 154 constituting the source lines SL areformed above the tungsten layers 152 to interpose the silicon dioxidelayer 156 (interlayer insulating layer) between them such that thecopper layers 154 extend in the forward and rearward direction. In thecross-section taken along C-C′, the copper layer 154 is connected to thetitanium/titanium nitride layer 149 (adhesive layer). The connectingportion of the copper layer 154 constitutes a contact 153 (contact C1 inFIG. 3). A titanium/titanium nitride layer may be formed as an adhesivelayer at a boundary region between the copper layer 154 and the silicondioxide layer 156, although not shown.

In the cross-section taken along C-C′, a copper layer 162 constitutingthe bit line BL is formed above the copper layer 154 to interpose thesilicon dioxide layer 156 (interlayer insulating layer) between themsuch that the copper layer 162 extends in the rightward and leftwarddirection. In the cross-section taken along F-F,′ the copper layer 162is connected to the platinum silicide layer 136, and the connectingportion of the copper layer 162 constitutes a contact 161 (contact C2 inFIG. 3). In other words, in this region, the tantalum oxide layer 140,the tantalum nitride layer 142 and the tungsten layer 144 are removedand the bit line BL and the platinum silicide layer 136 (contact wireCL) are short-circuited via the contact 161. A titanium/titanium nitridelayer may be formed as an adhesive layer at a boundary region betweenthe copper layer 162 and the silicon dioxide layer 156, although notshown.

In the cross-section taken along C-C′, a polysilicon layer 160 whichderives from a manufacturing step is formed at a lower half portion ofthe region between the memory trenches. The thickness of the polysiliconlayer 160 is, for example, 250 nm. A Si₃N₄ layer 146 which derives froma manufacturing step is formed on the polysilicon layer 160 and thesilicon dioxide layer 132. The thickness of the Si₃N₄ layer 146 is, forexample, 50 nm.

[Characteristic of Resistance Variable Element]

FIG. 5 is a view showing an exemplary characteristic (relationshipbetween voltages and resistance values) of a resistance variable elementincluded in the nonvolatile memory device according to Embodiment 1 ofthe present invention.

As a resistance variable element exhibiting the characteristic of FIG.5, a resistance variable element was manufactured to include a lowerelectrode comprising platinum (50 nm thickness), a resistance variablelayer comprising tantalum oxide (0<x<2.5 when tantalum oxide isexpressed as TaO_(x)), and an upper electrode comprising tantalumnitride (100 nm thickness) and having an electrode area of 0.5 μm×0.5μm. The tantalum oxide was deposited by sputtering (300 degrees C.).

Electric pulses of a pulse width 100 nsec were applied to themanufactured resistance variable element while changing the voltagegradually. After every application of the electric pulse, a voltage of50 mV was applied to the resistance variable element and a current wasmeasured, thus obtaining resistance values of the resistance variableelement. Plots in FIG. 5 indicate the voltages (voltages generatedbetween the upper electrode and the lower electrode) actually applied tothe resistance variable element. The polarity of the voltages isindicated by an electric potential of the lower electrode on the basisof the upper electrode. To be specific, the polarity was regarded asplus when the electric potential of the lower electrode was higher thanthe electric potential of the upper electrode.

As shown in FIG. 5, when the applied voltages were below −0.8V, theresistance variable element was changed from a high-resistance state(about 10⁵Ω) to a low-resistance state (about 10⁴Ω). On the other hand,when the applied voltages were above +0.8V, the resistance variableelement was changed from the low-resistance state to the high-resistancestate.

[Operation]

The outline of the operation of the nonvolatile memory device 100configured as described above will be described.

FIG. 6 is a timing chart showing an exemplary operation of thenonvolatile memory device according to Embodiment 1 of the presentinvention, in which FIG. 6( a) shows an operation in which “0” iswritten (resistance variable element RR is changed to a low-resistancestate) to a memory cell MC00 ₀₀, FIG. 6( b) shows an operation in which“1” is written (resistance variable element RR is changed to ahigh-resistance state) to the memory cell MC00 ₀₀, and FIG. 6( c) showsan operation in which data is read from the memory cell MC00 ₀₀. In thisembodiment, an event that the resistance variable element RR is in alow-resistance state (LR) is allocated to data “0,” while an event thatthe resistance variable element RR is in a high-resistance state (HR) isallocated to data “1.”

In FIG. 6( a), V1indicates a voltage output from the low-resistancestate attaining voltage generating circuit 122. In the case of elementhaving the characteristic of FIG. 5, for example, V1may be +1.5V(positive voltage larger in absolute value than −0.8V which is athreshold which enables the low-resistance state to be attained in thecharacteristic of FIG. 5).

In FIG. 6( b), V2indicates a voltage output from the high-resistancestate attaining voltage generating circuit 124. In the case of elementhaving the characteristic of FIG. 5, for example, V2may be +1.5V(positive voltage larger in absolute value than +1.2V which is athreshold which enables the high-resistance state to be attained in thecharacteristic of FIG. 5).

In FIG. 6( c), Vread is a read voltage generated in the sense amplifier120. In the case of element having the characteristic of FIG. 5, forexample, Vread may be +0.5V (positive voltage smaller in absolute valuethan +0.8V which is a low-resistance state disturb boundary voltage[upper limit voltage at which the resistance value of the resistancevariable element in the low-resistance state does not change] in FIG.5).

VDD in FIG. 6 corresponds to an electric power supply voltage suppliedto the nonvolatile memory element 100 from outside, and is, for example,+4.5V.

When data “0” is written to the resistance variable element RR(resistance variable element RR is changed to the low-resistance state),as shown in FIG. 6( a), initially, the voltage of a selected bit lineBL0 and a voltage of a selected source line SL0 ₀ are set to 0V (GND).Other bit lines BL and other source lines SL are placed in ahigh-impedance state. Then, a voltage of a selected word line WL0 ₀ isset to VDD. Then, the voltage of the selected source line SL0 ₀ is setto V1 for a specified time and then is returned to 0V. That is, arectangular voltage pulse (electric pulse) is applied to the selectedsource line SL0 ₀. Thus, a voltage of −V1 (−1.5V) is applied to thefirst electrode E1 (lower electrode) on the basis of the secondelectrode E2 (upper electrode) between the electrodes of the resistancevariable element RR included in the memory cell MC00 ₀₀. As a result,the resistance variable element RR changes from the high-resistancestate to the low-resistance state. Thereafter, the voltage of theselected word line WL0 ₀ is set to 0V and a write operation of data “0”is completed.

When data “1” is written to the resistance variable element RR(resistance variable element RR is changed to the high-resistancestate), as shown in FIG. 6( b), initially, the voltage of a selected bitline BL0 and the voltage of a selected source line SL0 ₀ are set to 0V(GND). Other bit lines BL and other source lines SL are placed in ahigh-impedance state. Then, the voltage of a selected word line WL0 ₀ isset to VDD. Then, the voltage of the selected bit line BL0 is set to V2for a specified time and then is returned to 0V. That is, a rectangularvoltage pulse (electric pulse) is applied to the selected bit line BL0.Thus, a voltage of +V2 (+1.5V) is applied to the first electrode E1(lower electrode) on the basis of the second electrode E2 (upperelectrode) between the electrodes of the resistance variable element RRincluded in the memory cell MC00 ₀₀. As a result, the resistancevariable element RR changes from the low-resistance state to thehigh-resistance state. Thereafter, the voltage of the selected word lineWL0 ₀ is set to 0V and a write operation of data “1” is completed.

The address input circuit 108 receives address signals from an externalcircuit (not shown) and outputs row address signals to the columndecoder 102 and column address signals to the row decoder 104 based onthe address signals. The address signals are signals indicating addressof a specified memory cell selected from among a plurality of memorycells.

In a write cycle of data, the control circuit 110 outputs to the writecircuit 116, a write signal for causing application of a write voltage,according to the input data Din input to the data input/output circuit114.

The column decoder 102 receives row address signals output from theaddress input circuit 108, and the row decoder 104 applies apredetermined voltage to a word line selected from among a plurality ofword lines, based on the row address signals. In the same manner, thecolumn decoder 102 receives row address signals output from the addressinput circuit 108, and applies a predetermined voltage to a source lineselected from among a plurality of source lines, based on the rowaddress signals.

The row decoder 104 receives column address signals output from theaddress input circuit 108, selects one from among the plurality of bitlines, based on the column address signals and applies a write voltageor a read voltage to the selected bit line.

Receiving the write signal output from the control circuit 110, thewrite circuit 116 outputs to the row decoder 104 a signal for causingapplication of a write voltage to the selected bit line. The writeelectric power supply 112 includes a low-resistance state attaining LRelectric power supply 122 and a high-resistance state attaining HRelectric power supply 124. The outputs of the low-resistance stateattaining LR electric power supply 122 and the high-resistance stateattaining HR electric power supply 124 are each input to the row decoder104 and the write circuit 116.

When data is read from the resistance variable element RR, as shown inFIG. 6( c), initially, the voltage of a selected bit line BL0 and thevoltage of a selected source line SL0 ₀ are set to 0V (GND). Other bitlines BL and other source lines SL are placed in a high-impedance state.Then, the voltage of a selected word line WL0 ₀ is set to VDD. Then, thevoltage of the selected bit line BL0 is set to Vread for a specifiedtime and then is returned to 0V. This is accomplished by feeding avoltage from a clamping circuit 118 to the selected bit line BL0. Thesense amplifier 120 detects a value of a current flowing through theselected memory cell MC00 ₀₀ to determine whether the resistancevariable element RR is in the low-resistance state (data is “0”) or inthe high-resistance state (“data” is 1). Thereafter, the voltage of theselected word line WL0 ₀ is set to 0V, thus completing a read operationof the data.

[Manufacturing Method]

FIGS. 7 to 42 are views showing the steps of manufacturing thenonvolatile memory device according to Embodiment 1 of the presentinvention. Steps other than those shown in FIGS. 7 to 42 are necessaryto manufacture the nonvolatile memory device 100, but well-known stepsmay be used as these steps and will not be described

FIGS. 7 and 8 are a top plan view and cross-sectional views,respectively, showing the step of forming the polysilicon layer on theP-type silicon substrate. FIG. 8( a) is a cross-sectional view taken inthe direction of arrows along A-A′ of FIG. 7, FIG. 8( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.7, FIG. 8( c) is a cross-sectional view taken in the direction of arrowsalong C-C′ of FIG. 7, FIG. 8(d) is a cross-sectional view taken in thedirection of arrows along D-D′ of FIG. 7, FIG. 8( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.7, and FIG. 8( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 7.

In a step (step S1) of forming the polysilicon layer over the P-typesilicon substrate, polysilicon is deposited over the P-type siliconsubstrate comprising the P-type silicon layer 130 by, for example, CVD,thereby forming the polysilicon layer 160. The height of a dummy gate isdesirably implemented by a layer thickness optimized for a process, inview of a dry etching property, etc.

FIGS. 9 and 10 are a top plan view and cross-sectional views,respectively, showing the step of etching the P-type silicon substrateand the polysilicon layer to form STI. FIG. 10( a) is a cross-sectionalview taken in the direction of arrows along A-A′ of FIG. 9, FIG. 10( b)is a cross-sectional view taken in the direction of arrows along B-B′ ofFIG. 9, FIG. 10( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 9, FIG. 10( d) is a cross-sectional view takenin the direction of arrows along D-D′ of FIG. 9, FIG. 10( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.9, and FIG. 10( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 9.

In a step (step S2) of etching the P-type silicon substrate and thepolysilicon layer to form the trench 163 into which the STI is filled, adesired trench is formed by a patterning step using a mask.

FIGS. 11 and FIG. 12 are a top plan view and cross-sectional view,respectively, showing the step of filling silicon dioxide into thetrench to form STI. FIG. 12( a) is a cross-sectional view taken in thedirection of arrows along A-A′ of FIG. 11, FIG. 12( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.11, FIG. 12( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 11, FIG. 12( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 11, FIG. 12( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.11, and FIG. 12( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 11.

In a step (step S3) of filling silicon dioxide into the trench to formthe STI, silicon dioxide (SiO₂) (HDP-NSG layer) is deposited by HDP-CVD(600 nm) to fill the trench 163 formed in step S2, and is removed toreach the upper end surface of the polysilicon layer 160 by CMP, therebyforming the silicon dioxide layer 130.

FIG. 13 and FIG. 14 are a top plan view and cross-sectional views,respectively, showing the step of forming a Si₃N₄ layer to cover thesilicon dioxide layer and the polysilicon layer. FIG. 14( a) is across-sectional view taken in the direction of arrows along A-A′ of FIG.13, FIG. 14( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 13, FIG. 14( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 13, FIG. 14( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.13, FIG. 14( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 13, and FIG. 14( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 13.

In a step (step S4) of forming the Si₃N₄ layer to cover the silicondioxide layer and the polysilicon layer, Si₃N₄ is deposited over theentire surface by CVD to form the Si₃N₄ layer 146.

FIG. 15 and FIG. 16 are a top plan view and cross-sectional views,respectively, showing the step of forming the memory trench. FIG. 16( a)is a cross-sectional view taken in the direction of arrows along A-A′ ofFIG. 15, FIG. 16( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 15, FIG. 16( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 15, FIG. 16( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.15, FIG. 16( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 15, and FIG. 16( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 15.

In a step (step S5) of forming the memory trench, the Si₃N₄ layer 146,the polysilicon layer 160 and the silicon dioxide layer 132 are removedat predetermined widths and intervals, to form the memory trenches 164extending in the upward and downward direction (second direction) ofFIG. 15. The bottom surface of the memory trench is flat and itsposition is controlled to be coplanar with the bottom surface of thepolysilicon layer 160. The rightmost trench 164, among the five memorytrenches 164 shown in FIG. 16( a), is the contact wire trench 166.

FIG. 17 and FIG. 18 are a top plan view and cross-sectional views,respectively, showing the step of implanting phosphorous atoms (P) intoa region of the bottom surface of each memory trench, where the P-typesilicon substrate is exposed. FIG. 18( a) is a cross-sectional viewtaken in the direction of arrows along A-A′ of FIG. 17, FIG. 18( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.17, FIG. 18( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 17, FIG. 18( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 17, FIG. 18( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.17, and FIG. 18( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 17.

In a step (step S6) of implanting phosphorous atoms (P) into the regionof the bottom surface of each memory trench where the P-type siliconsubstrate is exposed, the phosphorous atoms (P) are implanted into thebottom surface of the memory trench 164 formed in step S5 with a lowenergy, by ion implantation, and the P-implanted region 134 is formed byhigh-speed annealing. The phosphorous atoms are implanted only to aregion of the bottom surface of the memory trench 164 where the P-typesilicon substrate layer 130 is exposed, thereby forming the P-implantedregion 134. The phosphorous atoms are not implanted to a region of thebottom surface of the memory trench 164 where the silicon dioxide layer132 is exposed, and thus, the P-implanted region 134 is not formedthere. Therefore, the P-implanted region 134 is formed over the entirebottom surface of the contact wire trench 166. In contrast, theP-implanted regions 134 are formed like islands at specified intervalson the bottom surface of the other memory trenches 164 (see FIG. 17).Arsenic (As) atoms may be implanted instead of the phosphorous atoms.

FIG. 19 and FIG. 20 are a top plan view and cross-sectional views,respectively, showing the step of forming Si₃N₄ portions (side walls) onright and left side walls of each memory trench. FIG. 20( a) is across-sectional view taken in the direction of arrows along A-A′ of FIG.19, FIG. 20( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 19, FIG. 20( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 19, FIG. 20( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.19, FIG. 20( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 19, and FIG. 20( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 19.

In a step (step S7) of forming Si₃N₄ portions (side walls) on the rightand left side walls of each memory trench, Si₃N₄ is deposited in 70 nmthickness over the entire surface by CVD, and further, Si₃N₄ adhering tothe region other than the side surfaces of the memory trench is removedby dry etching, thereby forming the Si₃N₄ portions 138.

FIG. 21 and FIG. 22 are a top plan view and cross-sectional views,respectively, showing the step of implanting phosphorous atoms (P) intoa region between a pair of Si₃N₄ portions formed on each memory trench,where the P-type silicon substrate is exposed. FIG. 22( a) is across-sectional view taken in the direction of arrows along A-A′ of FIG.21, FIG. 22( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 21, FIG. 22( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 21, FIG. 22( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.21, FIG. 22( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 21, and FIG. 22( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 21.

In a step (step S8) of implanting the phosphorous atoms (P) into theregion between the pair of Si₃N₄ portions formed on each memory trench,where the P-type silicon substrate is exposed, the phosphorous atoms (P)are implanted at a low energy into the region between the Si₃N₄ portions(side walls) formed in step S7 by ion implantation and further theP-implanted region 134 is rendered deeper by high-speed annealing.Similarly to step S6, the phosphorous atoms are not implanted to aregion of the bottom surface of the memory trench where the silicondioxide layer 132 is exposed, and therefore the P-implanted region 134is not formed there.

FIG. 23 and FIG. 24 are a top plan view and cross-sectional views,respectively, showing the step of forming a platinum silicide layer intoa region between the pair of Si₃N₄ portions formed on each memorytrench, where the P-implanted region is exposed. FIG. 24( a) is across-sectional view taken in the direction of arrows along A-A′ of FIG.23, FIG. 24( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 23, FIG. 24( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 23, FIG. 24( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.23, FIG. 24( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 23, and FIG. 24( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 23.

In a step (step S9) of forming a platinum silicide layer in a regionbetween the pair of Si₃N₄ portions formed on each memory trench, wherethe P-implanted region is exposed, initially, platinum is deposited onthe bottom surface of the memory trench by sputtering (condition: e.g.,5 nm). Then, platinum silicide is formed at a boundary region betweenthe P-implanted region 134 and the deposited platinum layer by annealing(condition: e.g., 500 degrees C., 10 minutes). In this way, the platinumsilicide layer 136 is formed. An unnecessary portion of the platinumlayer is removed by a standard process.

FIG. 25 and FIG. 26 are a top plan view and cross-sectional views,respectively, showing the step of forming a tantalum oxide layer and atantalum nitride layer over an entire surface including side surfacesand a bottom surface of each memory trench. FIG. 26( a) is across-sectional view taken in the direction of arrows along A-A′ of FIG.25, FIG. 26( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 25, FIG. 26( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 25, FIG. 26( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.25, FIG. 26( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 25, and FIG. 26( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 25.

In a step (step S10) of forming the tantalum oxide layer and thetantalum nitride layer over the entire surface of each memory trench,including the side surfaces and the bottom surfaces, the tantalum oxideis deposited to form the tantalum oxide layer 140 by sputtering (e.g.,in reactive sputtering, the oxygen content can be made higher by settingthe oxygen flow rate higher during the deposition, in this embodiment,oxygen content is about 72 atm % under conditions of argon 34 sccm,oxygen 24 sccm, and power 1.6 kW). Then, by sputtering in argon andnitrogen gas atmosphere using a tantalum target, i.e., by reactivesputtering, tantalum nitride is deposited to form the tantalum nitridelayer 142. In this case, the thickness of the tantalum oxide layer isdetermined so that the thickness of the side walls is properly ensured(e.g., 3 nm) in view of a level difference covering ratio (ratio ofdimension between the side walls and the flat region). When the leveldifference covering ratio is, for example, 10%, the tantalum oxide isdeposited so that the flat region (including the bottom surface of thememory trench) is 30 nm. In this case, the thickness of the tantalumoxide layer 140 on the side walls is about 3 nm.

FIG. 27 and FIG. 28 are a top plan view and cross-sectional views,respectively, showing the step of removing the tantalum oxide layer andthe tantalum nitride layer except for a portion of the tantalum oxidelayer and a portion of the tantalum nitride layer which are presentinside the memory trench. FIG. 28( a) is a cross-sectional view taken inthe direction of arrows along A-A′ of FIG. 27, FIG. 28( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.27, FIG. 28( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 27, FIG. 28( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 27, FIG. 28( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.27, and FIG. 28( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 27.

In a step (step S11) of removing the tantalum oxide layer and thetantalum nitride layer except for a portion of the tantalum oxide layerand a portion of the tantalum nitride layer which are present inside thememory trench, the tantalum oxide layer 140 and the tantalum nitridelayer 142 except for a portion of the tantalum oxide layer 140 and aportion of the tantalum nitride layer 142 which are present inside thememory trench, are removed. In this case, the upper end surface of thetantalum oxide layer 140 and the upper end surface of the tantalumnitride layer 142 are controlled to be lower than the upper end surfaceof the Si₃N₄ layer 146 by increasing a polishing pressure or polishingtime of CMP. This is achieved by etch back instead of adjusting theconditions of CMP.

FIG. 29 and FIG. 30 are a top plan view and cross-sectional views,respectively showing the step of forming a tungsten layer into thetrench formed inside the tantalum nitride layer and forming the silicondioxide layer into a recess. FIG. 30( a) is a cross-sectional view takenin the direction of arrows along A-A′ of FIG. 29, FIG. 30( b) is across-sectional view taken in the direction of arrows along B-B′ of FIG.29, FIG. 30( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 29, FIG. 30( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 29, FIG. 30( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.29, and FIG. 30( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 29.

In a step (step S12) of forming the tungsten layer into the trenchformed inside the tantalum nitride layer and forming the silicon dioxidelayer into the recess, a tungsten layer 144 is formed to fill the trenchformed inside the tantalum nitride layer 142 to extend in the forwardand rearward direction. This is performed by CVD and CMP. Then, silicondioxide is filled into the recess defined by the Si₃N₄ portions 138(side walls), the tantalum oxide layer 140, the tantalum nitride layer142, and the tungsten layer 144, to form the silicon diode layer 148.This is accomplished by deposition of TEOS (about 50 nm) by CVD and byconducting CMP.

FIG. 31 and FIG. 32 are a top plan view and cross-sectional views,respectively, showing the step of forming the silicon dioxide layer overthe entire surface and forming the trench into which the word line isfilled. FIG. 32( a) is a cross-sectional view taken in the direction ofarrows along A-A′ of FIG. 31, FIG. 32( b) is a cross-sectional viewtaken in the direction of arrows along B-B′ of FIG. 31, FIG. 32( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.31, FIG. 32( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 31, FIG. 32( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 31, and FIG. 32( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 31.

In a step (step S13) of forming the silicon dioxide layer over theentire surface and forming the trench into which the word wire WL isfilled, TEOS oxide is deposited by CVD and a part of silicon dioxide isremoved by etching using a mask to form the trench 168 into which theword line WL is filled, thereby exposing a portion of the Si₃N₄ layer146 where the control electrode T3 (gate) of the transistor is formed(see FIG. 31).

FIG. 33 and FIG. 34 are a top plan view and cross-sectional views,respectively, showing the step of forming a hole into which the controlelectrode (gate) of the transistor is filled. FIG. 34( a) is across-sectional view taken in the direction of arrows along A-A′ of FIG.33, FIG. 34( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 33, FIG. 34( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 33, FIG. 34( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.33, FIG. 34( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 33, and FIG. 34( f) is a cross-sectional viewtaken in the direction of arrows along F-F′ of FIG. 33.

In a step (step S14) of forming the hole into which the controlelectrode (gate) of the transistor is filled, a portion of the Si₃N₄layer 146 where the control electrode T3 (gate) of the transistor isformed is removed by dry etching using a mask. The polysilicon layer 160is dissolvable in an alkaline solution such as TMAH. Alternatively,chemical dry etching using CF₄ and O₂ may be used. In this way, a hole170 into which the control electrode (gate) of the transistor is filledis formed.

FIG. 35 and FIG. 36 are a top plan view and cross-sectional views,respectively showing the step of forming the word line and the controlelectrode (gate) of the transistor. FIG. 36( a) is a cross-sectionalview taken in the direction of arrows along A-A′ of FIG. 35, FIG. 36( b)is a cross-sectional view taken in the direction of arrows along B-B′ ofFIG. 35, FIG. 36( c) is a cross-sectional view taken in the direction ofarrows along C-C′ of FIG. 35, FIG. 36( d) is a cross-sectional viewtaken in the direction of arrows along D-D′ of FIG. 35, FIG. 36( e) is across-sectional view taken in the direction of arrows along E-E′ of FIG.35, and FIG. 36( f) is a cross-sectional view taken in the direction ofarrows along F-F′ of FIG. 35.

In a step (step S15) of forming the word line and the control electrodeT3 (gate) of the transistor, initially, a titanium/titanium nitridelayer 150 (adhesive layer) is deposited by sputtering, and further thetungsten layer 152 (word line WL and control terminal T3) is formed byplating.

FIG. 37 and FIG. 38 are a top plan view and cross-sectional views,respectively, showing the step of forming a trench into which the sourceline is filled and a hole into which a contact is filled. FIG. 38( a) isa cross-sectional view taken in the direction of arrows along A-A′ ofFIG. 37, FIG. 38( b) is a cross-sectional view taken in the direction ofarrows along B-B′ of FIG. 37, FIG. 38( c) is a cross-sectional viewtaken in the direction of arrows along C-C′ of FIG. 37, FIG. 38( d) is across-sectional view taken in the direction of arrows along D-D′ of FIG.37, FIG. 38( e) is a cross-sectional view taken in the direction ofarrows along E-E′ of FIG. 37, and FIG. 38( f) is a cross-sectional viewtaken in the direction of arrow along F-F′ of FIG. 37.

In a step (step S16) of forming the trench into which the source line SLis filled and forming the hole into which the contact C1 is filled,silicon dioxide is deposited by thermal oxidation (condition: e.g., 10nm), and then a part of the deposited silicon dioxide is removed byetching using a mask, thereby forming the trench 172 into which thesource line SL is filled and forming the hole 174 into which the contactC1 is filled.

FIG. 39 and FIG. 40 are a top plan view and cross-sectional views,respectively, showing the step of forming the source line and thecontact. FIG. 40( a) is a cross-sectional view taken in the direction ofarrows along A-A′ of FIG. 39, FIG. 40( b) is a cross-sectional viewtaken in the direction of arrows along B-B′ of FIG. 39, FIG. 40( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.39, FIG. 40( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 39, FIG. 40( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 39, and FIG. 40( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 39.

In a step (step S17) of forming the source line and the contact, copperis filled into the trench 172 and the hole 174 formed in step S16 bydamascene process and an unnecessary portion of copper is removed byCMP. As a result, the copper layer 154 and the contact 153 (contact C1in FIG. 3) are formed.

FIG. 41 and FIG. 42 are a top plan view and cross-sectional views,respectively showing the step of forming the bit line and a contact.FIG. 42( a) is a cross-sectional view taken in the direction of arrowsalong A-A′ of FIG. 41, FIG. 42( b) is a cross-sectional view taken inthe direction of arrows along B-B′ of FIG. 41, FIG. 42( c) is across-sectional view taken in the direction of arrows along C-C′ of FIG.41, FIG. 42( d) is a cross-sectional view taken in the direction ofarrows along D-D′ of FIG. 41, FIG. 42( e) is a cross-sectional viewtaken in the direction of arrows along E-E′ of FIG. 41, and FIG. 42( f)is a cross-sectional view taken in the direction of arrows along F-F′ ofFIG. 41.

In a step (step S18) of forming the bit line and the contact, TEOS isdeposited over the entire surface by CVD to cover the copper layer 154and the contact 153 and a part of silicon dioxide is removed by etchingusing a mask, thereby forming the trench into which the bit line BL isfilled and the hole into which the contact C2 is filled. Copper isfilled into the trench and the hole by damascene process and anunnecessary portion of copper is removed by CMP. In this way, the copperlayer 162 and the contact 161 (contact C2 in FIG. 3) are formed.

Through the above steps, the memory block shown in FIGS. 3 and 4 ismanufactured. (FIG. 42 is identical to FIG. 4).

Modification Example

FIG. 43 is a block diagram showing an exemplary circuit configuration ofa nonvolatile memory device 100′ according to Modification Example ofEmbodiment 1 of the present invention. As shown in FIG. 43, the bothends of each series path may be connected to the bit line (third wire)for each memory block.

Such a configuration is attained by adding one contact wire CL at theleft of SL0 ₀ and by connecting the contact wire CL to the bit line BL0via a contact C2, in the configuration of FIGS. 3 and 4. The contactwire to be added may be configured similarly to the contact wire ofEmbodiment 1. The specific configuration and details of themanufacturing method are obvious to persons skilled in the art and willnot be described.

In such a configuration, since an electric potential propagates from theboth sides of the series path, wire delay can be suppressed moreeffectively.

In this modification example, the configuration other than theconnecting relation between the series path SP and the bit line BL issimilar to that described in the embodiment shown in FIG. 1. Therefore,in FIG. 43, the same constituents as those in FIG. 1 are designated bythe same reference numerals and names and these constituents will not bedescribed repetitively.

Embodiment 2

FIG. 44 is a block diagram showing an exemplary circuit configuration ofa nonvolatile memory device according to Embodiment 2 of the presentinvention.

A nonvolatile memory device 200 of Embodiment 2 includes an electricpower supply circuit 113 for applying voltages to the resistancevariable element included in each memory cell. The electric power supplycircuit 113 is configured to change output voltages, according to thenumber of transistors TR included in a portion of the series path SPassociated with a selected memory cell MC, from the connecting point ofthe associated series path SP and the associated bit line (third wire)to the first electrode E1 of the selected memory cell MC.

To be more specific, the nonvolatile memory device 200 includes anelectric power supply circuit 113 replacing the electric power supplycircuit 112 in the nonvolatile memory device 100 of FIG. 1, and a firsthigh-resistance state attaining voltage generating circuit 125, a secondhigh-resistance state attaining voltage generating circuit 126, a thirdhigh-resistance state attaining voltage generating circuit 127 and afourth high-resistance state attaining voltage generating circuit 128,which replace the high-resistance state attaining voltage circuit 124 inthe nonvolatile memory device 100 of FIG. 1. The other constituents areidentical to those of the nonvolatile memory device 100 of FIG. 1.Therefore, in FIG. 44, the same constituents as those in FIG. 1 aredesignated by the same reference numerals and names and will not bedescribed repetitively.

The first high-resistance state attaining voltage generating circuit 125outputs a voltage V2₀ (first high-resistance state attaining voltage)applied to a selected bit line BL to change a memory cell MC belongingto the first column from the left in the memory block to ahigh-resistance state. Transistors included in a portion of the seriespath SP, connecting the first electrode E1 of the resistance variableelement RR included in the memory cell to the bit line BL is four innumber.

The second high-resistance state attaining voltage generating circuit126 outputs a voltage V2₁ (second high-resistance state attainingvoltage) applied to a selected bit line BL to change a memory cell MCbelonging to the second column from the left in the memory block to ahigh-resistance state. Transistors included in a portion of the seriespath SP, connecting the first electrode E1 of the resistance variableelement RR included in the memory cell to the bit line BL is three innumber.

The third high-resistance state attaining voltage generating circuit 127outputs a voltage V2₂ (third high-resistance state attaining voltage)applied to a selected bit line BL to change a memory cell MC belongingto the third column from the left in the memory block to ahigh-resistance state. Transistors included in a portion of the seriespath SP, connecting the first electrode E1 of the resistance variableelement RR included in the memory cell to the bit line BL is two innumber.

The fourth high-resistance state attaining voltage generating circuit128 outputs a voltage V2₃ (fourth high-resistance state attainingvoltage) applied to a selected bit line BL to change a memory cell MCbelonging to the fourth column from the left in the memory block to ahigh-resistance state. Transistors included in a portion of the seriespath SP, connecting the first electrode E1 of the resistance variableelement RR included in the memory cell to the bit line BL is one innumber.

The voltage V2₀, the voltage V2₁, the voltage V2₂ and the voltage V2₃are set so that the voltage applied between the electrodes of theresistance variable element RR is equal irrespective of the location ofthe resistance variable element RR within the memory block in view of asubstrate bias effect and according to the path length (the number oftransistors included in the shortest series path connecting theresistance variable element to the bit line) of the shortest series pathconnecting the first electrode E1 of the memory cell belonging to eachcolumn, to the bit line BL.

A substrate bias effect is not substantially occurred in a selectedtransistor in a case where a selected source line SL is placed at a highelectric potential and a selected bit line BL is placed at a lowelectric potential (e.g., ground potential) (in the example ofEmbodiment 1, the memory cell is changed to the low-resistance state asshown in FIG. 6( a)), and therefore substantially whole amount of thefed voltage is applied to the both electrodes of the resistance variableelement RR in the memory cell. On the other hand, a reverse bias becauseof a substrate bias effect is substantially occurred in a selectedtransistor in a case where a selected source line SL is placed at a lowelectric potential and a selected bit line BL is placed at a highelectric potential (in the example of Embodiment 1, the memory cell ischanged to the high-resistance state as shown in FIG. 6( b)), andtherefore the voltage actually applied between the both electrodes ofthe resistance variable element RR in the memory cell is smaller inmagnitude than the voltage fed between the selected source line SL andthe selected bit line BL.

FIG. 45 is a view showing a circuit used to simulate an electricpotential drop because of the substrate bias effect. In FIG. 45, A-Trdesignates a control transistor located between the electric powersupply circuit and the memory cells. Tr₀˜Tr₁₅ designate transistorsconnected to the memory cells, respectively. V_(E0)˜V_(E15) designatevoltages on the source line, respectively, in the case where V_(D)(V_(D0)˜V_(D15)) of the transistors constituting the memory cells are0V. FIG. 46 is a view showing result of the electric potential drops ofV_(D) (V_(D0)˜V_(D15)) of the transistors because of the substrate biaseffect, which is a obtained by conducting simulation, based on thecircuit diagram of FIG. 45. The transistors Tr₀˜Tr₁₅ and A-Tr used inthe simulation have an identical configuration and are 3.3V based NMOStransistors (gate width W=440 nm, gate length L=380 nm, and a gate oxidelayer thickness=9.7 nm).

As shown in FIG. 45, transistors are arranged successively in a lineshape such that the first main terminal (source/drain) of one ofadjacent transistors is connected to the second main terminal(source/drain) of the other transistor. The control terminals (gates) ofthe respective transistors are connected to each other and is appliedwith an equal electric potential (V_(G)). The lower electrode of theresistance variable element is connected to each connecting portion(main terminal) of adjacent two transistors. It is supposed that theresistance variable element is not connected to the right main terminalof the rightmost transistor Tr₀, but to the bit line BL, among thetransistors connected to the memory cells. It is also supposed that theupper electrodes of the resistance variable elements are electricallygrounded.

In this configuration, the voltage applied to the bit line connected tothe main terminal of A-Tr is expressed as V_(BL), and the voltagesactually applied to the first to fifteenth resistance variable elementsfrom the right are expressed as V_(D0)˜V_(D15), respectively. WhenV_(BL)=+1.8V, the electric potentials of V_(D0)˜V_(D15) are lower as theassociated nodes are more distant from A-Tr. V_(D0)˜V_(D15) are variableaccording to the magnitude of V_(G). FIG. 46 is a view showing therelationship between V_(D0), V_(D3), V_(D7), and V_(D15), and V_(G).When V_(G)=VDD=+4.5V, V_(D0) to V_(D3) are not less than +1.2V. Tochange the resistance variable element to the high-resistance state, itis necessary to apply a positive voltage larger in absolute value than+1.2V which is a threshold for attaining the high-resistance state inthe example of FIG. 5. Therefore, in accordance with the elementcharacteristic of FIG. 5 and the above voltage relation, up to fourmemory cells can be connected to one series path. By reducingON-resistance of each transistor or reducing the substrate bias effect,more memory cells can be connected to one series path. For the abovementioned reason, in Embodiment 1, four memory cells are connected toone series path (four memory cells are included in one row within thememory block). By regulating V_(G) or V_(BL), more memory cells can beconnected to one series path.

The degree of a voltage drop due to the substrate bias effect isdifferent according to the location on the series path (the number oftransistors included in a path connecting the resistance variableelements to the bit line) so long as V_(BL) is constant, and therefore,the voltage actually applied to the resistance variable element changes.In order to uniformize the respective resistance values after writingand to prevent an unnecessary voltage stress from being applied to theresistance variable element, the applied voltage is desirably constantirrespective of the location of the memory cell on the series path. Tothis end, it is desired that V_(BL) be regulated preliminarily so thatthe voltage applied between the both electrodes of the resistancevariable element RR is equal irrespective of the location of theresistance variable element within the memory block according to thepath length of the shortest series path connecting the first electrodeE1 of the memory cell to the bit line BL (the number of transistorsincluded in the shortest series path connecting the resistance variableelement to the bit line). In this embodiment, such control is achievedby using the first high-resistance state attaining voltage generatingcircuit 125, the second high-resistance state attaining voltagegenerating circuit 126, the third high-resistance state attainingvoltage generating circuit 127 and the fourth high-resistance stateattaining voltage generating circuit 128 to change V_(BL) to V2₀˜V2₃ asdescribed above according to the location of the memory cell.

In accordance with the above configuration, the voltage applied betweenthe electrodes of the resistance variable element RR can be madeconstant irrespective of the location of the memory cell MC, therespective resistance values after writing can be more uniformized, andan unnecessary voltage stress applied to the resistance variable elementcan be suppressed more effectively, as compared to the configurationconventionally used.

Modification Example

In this embodiment, modification example similar to that of Embodiment 1can be made.

Numeral modifications and alternative embodiments of the presentinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, the description is to be construedas illustrative only, and is provided for the purpose of teaching thoseskilled in the art the best mode of carrying out the invention. Thedetails of the structure and/or function may be varied substantiallywithout departing from the spirit of the invention.

INDUSTRIAL APPLICABILITY

A nonvolatile memory device of the present invention is useful as anonvolatile memory device capable of implementing a memory cell of 4F²while effectively suppressing a current flowing through an unselectedmemory cell.

REFERENCE SIGNS LIST

100, 100′ nonvolatile memory device

102 column decoder

104 row decoder

106 memory cell array

108 address input circuit

110 control circuit

112 electric power supply circuit

114 data input/output circuit

116 write circuit

118 clamping circuit

120 sense amplifier

122 low-resistance state attaining voltage generating circuit

124 high-resistance state attaining voltage generating circuit

125 first high-resistance state attaining voltage generating circuit

126 second high-resistance state attaining voltage generating circuit

127 third high-resistance state attaining voltage generating circuit

128 fourth high-resistance state attaining voltage generating circuit

130 P-type silicon substrate layer

132 silicon dioxide layer

134 P-implanted region

136 platinum silicide layer

138 Si₃N₄ portions

140 tantalum oxide layer

142 tantalum nitride layer

144 tungsten layer

146 Si₃N₄ layer

148 silicon dioxide layer

149 titanium/titanium nitride layer

150 titanium/titanium nitride layer

152 tungsten layer

153 contact

154 copper layer

156 silicon dioxide layer

158 silicon dioxide layer

160 polysilicon layer

161 contact

162 copper layer

163 trench

164 memory trench

166 contact wire trench

168 trench

170 hole

172 trench

174 hole

200 nonvolatile memory device

BL bit line

CL contact wire

C1, C2 contacts

D/S drain/source

E1 first electrode

E2 second electrode

G gate

MC memory cell

RR resistance variable element

SL source line

T1 first main terminal (drain/source)

T2 second main terminal (drain/source)

T3 control terminal (gate)

TR transistor

VR resistance variable layer

WL word line

1. A nonvolatile memory device comprising: a plurality of first wiresextending in parallel with each other in a first direction within afirst plane; a plurality of second wires extending in parallel with eachother in a second direction within a second plane parallel to the firstplane such that the plurality of second wires three-dimensionally crossthe plurality of first wires, respectively; and memory cells provided torespectively correspond to three-dimensional cross-points of the firstwires and the second wires; each of the memory cells including onetransistor and one resistance variable element; the transistor includinga first main terminal, a second main terminal and a control terminal;the resistance variable element including a first electrode, a secondelectrode and a resistance variable layer provided between the firstelectrode and the second electrode; the memory cells including aplurality of memory cells which are arranged along the first directionand configured such that a first main terminal of one of two adjacentmemory cells is connected to a second main terminal of the other memorycell, to form a series path extending in the first direction andsequentially connecting main terminals of the plurality of memory cellsin series; and each of the memory cells being configured such that: thecontrol terminal is connected to a first wire associated with the memorycell; the second electrode is a part of a second wire associated withthe memory cell or is connected to the second wire associated with thememory cell; and the first electrode is a part of a series pathassociated with the memory cell or is connected to the series pathassociated with the memory cell.
 2. The nonvolatile memory deviceaccording to claim 1, further comprising: a plurality of third wiresextending in parallel with each other in the first direction; whereinthe plurality of memory cells arranged along the first directionconstitute a plurality of memory blocks each of which includes apredetermined number of memory cells arranged successively and theseries path is connected to the third wire for each of the memoryblocks.
 3. The nonvolatile memory device according to claim 2, whereinboth ends of the series path are connected to the third wire for each ofthe memory blocks.
 4. The nonvolatile memory device according to claim2, further comprising: an electric power supply circuit for applyingvoltages to the resistance variable element included in each of thememory cells; wherein the electric power supply circuit is configured tochange output voltages, according to the number of transistors includedin a portion of a series path associated with a selected memory cell,from a connecting point of the associated series path and the associatedthird wire to the first electrode of the selected memory cell.
 5. Thenonvolatile memory device according to claim 1, wherein each of thefirst main terminal and the second main terminal includes a silicidelayer; and the silicide layer constitutes the first electrode.
 6. Thenonvolatile memory device according to claim 5, wherein the silicidelayer comprises platinum silicide.